This invention is generally directed to airborne wind energy conversion systems and methods.
The classical work in the airborne wind energy conversion systems (AWECS) is the article by Miles L. Loyd “Crosswind Kite Power” (1979), in which the author disclosed a wind energy harvesting device, comprising a tethered wing, flying cross wind and harvesting wind energy, and transferring harvested energy to a ground based generator via motion of the tether. Crosswind motion of a wing is much more efficient, than downwind motion, allowing the wing to fly many times speed of the wind and harvest energy from an area, many times larger than the area of the wing. The article has also offered two ways of converting harvested mechanical energy into electrical energy.
In one of them, the electrical generator is on the ground and the tether is reeling out, transferring motion to the rotor of the generator. Systems, implementing this method are discussed in the U.S. Pat. Nos. 7,504,741 & 7,546,813 by Wrage et al, U.S. Pat. No. 8,080,889 by Ippolito et al, U.S. Pat. No. 6,523,781 by Ragner. Velocity of the lengthwise motion of the tether must be well below velocity of the wing. In such conditions, the tether is subject to the very high force, requiring thick tethers and creating very large torque in the ground equipment for useful power, thus rendering the whole system uneconomical.
In another method, the generator is airborne and its rotor is coaxial with the propeller, driven by relative air flow. This method is discussed in the U.S. Pat. No. 3,987,987 by Payne et al., U.S. Pat. No. 8,109,711 by Blumer et al. Among shortcomings of this method are large weight of the generator, carried onboard, large weight and limited flexibility of the tether, which is tasked with conducting electrical power from the generator to the ground.
The systems with downwind wing motion or with drag based (i.e., non-airfoil) airborne members are also worth mentioning. One such system is discussed in the U.S. Pat. No. 6,072,245 by Ockels. Aside of the shortcoming of the downwind wing motion, it forces the wings to approach the ground and uses a complex apparatus to prevent collision between the wings and the ground mechanisms.
This invention is directed to solving these shortcomings and providing a cost efficient AWECS. Certain airborne wind energy conversion systems with fast motion transfer were disclosed in PCT/US12/66331 and PCT/US13/30314 by Goldstein. Nevertheless, there is need in larger variety of cost efficient AWECS. This invention is directed to provide such variety.